By performing heat treatment on surface layer defects (COPs) of a silicon wafer in a non-oxidizing atmosphere, the surface layer COPs are eliminated. In the case of high-temperature heat treatment, a SiC jig is often used, and an environment in which a silicon single crystal wafer (hereinafter referred to simply as a silicon wafer) subjected to heat treatment is taken out of something contains oxygen and a carbonation product, which become a source of carbon contamination of the silicon wafer. The silicon wafer contaminated by carbon forms a defect in a device process and causes a leakage current or the like. Moreover, contaminated carbon becomes a carbon donor and becomes a cause of the generation of a Vth (threshold voltage) shift of a device and a device operating failure.
Thus, forming an oxide layer on a silicon wafer as the measures against carbon contamination of the silicon wafer is proposed in Patent Literature 1. However, although. this method is expected to have an effect to some extent as the measures against carbon contamination, the amount of carbon coming out from the SiC jig due to high-temperature oxidation is large and the above measures are not measures to suppress carbon generation itself from the source of carbon contamination, and therefore it is difficult to suppress reliably carbon contamination only with the above measures. Moreover, since a thick oxide film is formed on the front surface of the heat-treated wafer, removal of the oxide film and a polishing process are required. Furthermore, since the oxide film is formed at a high temperature, oxygen is implanted into a wafer surface layer and the defect size of a defect which has not been eliminated in a surface layer portion is increased due to a supply of oxygen, which becomes a cause of degradation of electrical characteristics.